The solo flight had been scheduled as a logical sequence to three dual-training missions following a year-long break from flying. The student was qualified and authorized to complete the occurrence flight in accordance with CARs and the FTU practices. During the solo training flight, the aircraft entered a spiral dive from which the student did not recover. The reason the aircraft entered the spiral dive and the student's inability to recover from the dive are not known. The initial roll manoeuvre, as observed on radar, and the subsequent stabilization of pitch and bank at constant angles support conclusions that the aircraft's control system was operating and that the pilot was conscious and manipulating the controls throughout the manoeuvre. Based on the described aircraft motion, it is likely that the student was applying a neutral aileron input and a forward control pressure to counter the progressive aft-movement of the control column, brought on by the increasing speed descent. Based on this analysis, it is likely that the student was attempting to centralize the controls as a element of his recovery procedure. A review of all the available medical records and reports revealed no indication of any pre-existing medical issue that would have adversely affected the pilot's ability to control the aircraft. However, the five-year medical validity period for the student pilot permit reduces the possibility of on-going early monitoring of a student pilot's medical status that a more frequent medical examination would permit. Although this student's ability to perform steep turns had been initially documented as weak, additional remedial dual instruction had been given to ensure the student's safe performance of the upper air sequences during solo practice. More recent review and evaluation of steep turns, stalls, and spiral dive recoveries re-affirmed the student's ability to perform these manoeuvres in a safe manner while recognizing that further practice would be necessary to improve the steep turn sequence up to the performance standards required of a private pilot license. Control continuity and pilot incapacitation have been eliminated as potential causes for this occurrence based on the witness descriptions of constant bank and pitch angles throughout the manoeuvre. Additionally, evaluations of broken control wheel components revealed that internal manufacturing voids identified throughout the plastic Piper control wheels do not appear to compromise the integrity of the component when subjected to FAR23testing. Although not related to this accident sequence, the SDR database shows that at least five control wheel breaks have occurred during aircraft operations; some of these breaks occurred outside the area that is being inspected as a result of AD69-22-02. Transport Canada's effort to improve this AD have been added to the Safety Action Taken section of this report. The Following Engineering Branch report was completed:Analysis The solo flight had been scheduled as a logical sequence to three dual-training missions following a year-long break from flying. The student was qualified and authorized to complete the occurrence flight in accordance with CARs and the FTU practices. During the solo training flight, the aircraft entered a spiral dive from which the student did not recover. The reason the aircraft entered the spiral dive and the student's inability to recover from the dive are not known. The initial roll manoeuvre, as observed on radar, and the subsequent stabilization of pitch and bank at constant angles support conclusions that the aircraft's control system was operating and that the pilot was conscious and manipulating the controls throughout the manoeuvre. Based on the described aircraft motion, it is likely that the student was applying a neutral aileron input and a forward control pressure to counter the progressive aft-movement of the control column, brought on by the increasing speed descent. Based on this analysis, it is likely that the student was attempting to centralize the controls as a element of his recovery procedure. A review of all the available medical records and reports revealed no indication of any pre-existing medical issue that would have adversely affected the pilot's ability to control the aircraft. However, the five-year medical validity period for the student pilot permit reduces the possibility of on-going early monitoring of a student pilot's medical status that a more frequent medical examination would permit. Although this student's ability to perform steep turns had been initially documented as weak, additional remedial dual instruction had been given to ensure the student's safe performance of the upper air sequences during solo practice. More recent review and evaluation of steep turns, stalls, and spiral dive recoveries re-affirmed the student's ability to perform these manoeuvres in a safe manner while recognizing that further practice would be necessary to improve the steep turn sequence up to the performance standards required of a private pilot license. Control continuity and pilot incapacitation have been eliminated as potential causes for this occurrence based on the witness descriptions of constant bank and pitch angles throughout the manoeuvre. Additionally, evaluations of broken control wheel components revealed that internal manufacturing voids identified throughout the plastic Piper control wheels do not appear to compromise the integrity of the component when subjected to FAR23testing. Although not related to this accident sequence, the SDR database shows that at least five control wheel breaks have occurred during aircraft operations; some of these breaks occurred outside the area that is being inspected as a result of AD69-22-02. Transport Canada's effort to improve this AD have been added to the Safety Action Taken section of this report. The Following Engineering Branch report was completed: During a student solo flight, the aircraft commenced a descending turn to the left and entered a spiral dive from which there was no recovery. The reason the aircraft entered the spiral dive and the reason that the student did not recover from it were not determined.Findings as to Causes and Contributing Factors During a student solo flight, the aircraft commenced a descending turn to the left and entered a spiral dive from which there was no recovery. The reason the aircraft entered the spiral dive and the reason that the student did not recover from it were not determined. A five-year medical validity period for the student pilot permit reduces the ongoing early monitoring of student pilot medical status. Although not causal in this accident, the TC SDR database shows that at least five control wheel breaks have occurred during aircraft operations; some of these breaks occurred outside the area being inspected as a result of AD69-22-02.Findings as to Risk A five-year medical validity period for the student pilot permit reduces the ongoing early monitoring of student pilot medical status. Although not causal in this accident, the TC SDR database shows that at least five control wheel breaks have occurred during aircraft operations; some of these breaks occurred outside the area being inspected as a result of AD69-22-02. Manufacturing voids identified throughout the plastic Piper control wheels do not appear to compromise the integrity of the control wheels when subjected to FAR23testing.Other Findings Manufacturing voids identified throughout the plastic Piper control wheels do not appear to compromise the integrity of the control wheels when subjected to FAR23testing. Safety Action Safety Action Taken Transport Canada reports that it has drafted a letter to the FAA highlighting two elements that may further improve the effectiveness of AD69-22-02 regarding Piper control wheel cracking: expanding the area to be inspected beyond the point where the pin enters the control wheel hub; and, changing the compliance interval for the inspection. The subject AD only requires that the inspection of the control wheel be completed within 25hours time in service from the effective date of the AD and thereafter, every 100hours since the last inspection. TC notes that many private aircraft operators in Canada do not fly 100hours in a year and may take up to five years to fly the required hours that would trigger AD compliance. Changing the AD compliance interval, to include both the 100hours time since the last inspection or annually would help mitigate the risk of a control wheel failure for those private operators.